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<DIV>Hi, I have been working on AC Optimal Power Flow for a while. The AC OPF is naturally a non-convex problem. The AMPL file that I have written works perfectly with all of the Mixed Integer Non-Linear solvers on the NEOS site. IEEE 5-Bus and 14-Bus are used to check the results.</DIV>
<DIV>The referees of the Journal that I had sent my paper, believed that these test systems are small and the methodology should be checked on a real system. Therefore I am testing the real power system of a country with 1388 buses and 1212 lines. </DIV>
<DIV>I have entered a Snap Shot of the network as the starting point and have run the program with all the possible assumptions but can't get any feasible solution.</DIV>
<DIV>When I use Couenne as the solver, I get the following results:</DIV>
<DIV><FONT color=#00007f>****************************************************************************** </FONT></DIV>
<DIV><FONT color=#00007f>Job 2379178 has finished.<BR>Job 2379178 sent to e032.chtc.wisc.edu<BR>password: tYaAJeBv<BR>---------- Begin Solver Output -----------<BR>Executing /opt/neos/Drivers/couenne-ampl/couenne-driver.py<BR>File exists<BR>You are using the solver couenne.<BR>Executing AMPL.<BR>processing data.<BR>processing commands.<BR><BR>Presolve eliminates 4268 constraints and 9191 variables.<BR>Adjusted problem:<BR>Error: Error at _cmdno 3 executing "solve" command<BR>3913 variables:<BR>Error: (file amplin, line 2727, offset 199919):<BR> 3329 nonlinear variables<BR>Error: can't open /tmp/neos-29505/at29512.sol<BR> 584 linear variables<BR>4547 constraints; 21611 nonzeros<BR> 4543 nonlinear constraints<BR> 4 linear constraints<BR>1 linear objective; 584 nonzeros.<BR><BR>couenne: <BR>ANALYSIS TEST: Problem size before reformulation: 3913 variables (0 integer), 4547 constraints.<BR>Problem size after reformulation: 26548 variables (0 integer),
3043 constraints.<BR> warning, tightened NLP is infeasible<BR>problem infeasible<BR> Error (512) in /opt/ampl/ampl -R amplin<BR>*******************************************************************************************</FONT></DIV>
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<LI>Can the limitaions on NEOS server be the reason of the infeasible solution?</LI>
<LI>Does reducing the size of the problem by ommitting some buses and lines can help to get a feasible solution?</LI></OL>
<DIV>I thank you in advance for your help.</DIV>
<DIV>Regards,</DIV>
<DIV>Mahbube</DIV>
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